But isn’t this exactly the mainstream intuition that the OP dissolves? My understanding:
a) Heritability measures don’t seem to make sense for really complex traits like intelligence.
b) Heritability measures are not stable outside the environmental conditions in which they were measured.
For instance, some people have sickle cell anemia, which helps them better survive malaria(but otherwise is slightly harmful). If you measure heritability of infant mortality in environment with malaria and then in environment without malaria you get opposite effects. You get a lighter case of malaria with it, so sickle cell probably positively correlates with intelligence if there’s malaria in the environment.
The findings from the Överkalix cohorts imply that grandparental access to food during their slow growth period can modify diabetes and all-cause mortality in grandchildren. Cardiovascular mortality on the other hand was associated with parental, but not grandparental, nutritional experience. The authors interpret their results11 as “proof-of-principle that a sex-specific male-line transgenerational effect exists in humans”, which they consider likely to be epigenetic rather than genetic, cultural or social. A summary of the Överkalix findings is available in19. Their findings have been discussed in renowned peer-reviewed journals20,21,22,23,24 and are cited over 2,000 times (October 2018).
I have this vague memory about reading an article claiming that grandparents’ access to food influenced their grandchildren’s height, moreso than their immediate childrens’, but I can’t seem to find it. Perhaps nonsense.
It is not that intuition. The mainstream intuition is that a high heritability means that variations in the thing that you’re measuring (height, SAT scores, infant mortality) is primarily affected by genetics and cannot be influenced by the environment. A better framing would say that high heritability means that variations in the thing that you’re measuring are not well explained by existing variation in the environment. To reframe, then, what I was going for above, a high heritibility is an upper bound on how much you can expect to improve a specific measure by playing around with existing policy levers, versus having to think outside the box and develop new policy levers.
So, again, pretend that SAT scores have a high measured variability in the US. (I think it’s actually closer to 50 than either extreme, but I don’t have off-hand an actual example of a measure that we might want to increase/reduce the variance of as a society that does have a high heritability.) We might look at nutrition, SES and education and ask whether we can manipulate these to significantly reduce the variance in height and/or SAT scores. Under the high heritability assumption, the answer is that this is very unlikely for both stats.
Again, this is without saying that high heritability means the existing policy levers are not having an effect right now. If we, as a country, stoppd feeding kids at age 5 and left them to fend for themselves, I would expect the survivors to be both shorter and have lower SAT scores than preceding generations. If we stopped sending kids to school, I would expect average SAT scores to drop and the variance to increase significantly. And nothing about heritability argues against any of that.
It also doesn’t mean that there are no policy levers that could have an effect. I am not biologist enough to know if the application of HGH to children on a large scale would increase average height, but what I can say is that heritability has nothing to say on the question, since it is currently an environmental variable with almost no variance itself.
Oops. Accidentally dropped a paragraph about whether you could increase height/SAT scores across the board with the existing policy levers. In that case, a high heritability doesn’t directly say that that’s unlikely, but you would at least have to expect to increase your policy setting to the point where most people are getting more of the nutrition or education or whatever than is currently a few standard deviations above average, since otherwise if less than that much of your policy was having an effect, you would expect to already see it in the heritability measurement. So heritability doesn’t say that feeding kids 10,000 calories a day or sending them to school for 12 hours a day won’t have effects on height/SAT scores, but as a general rule you’d be looking at such extreme interventions that it’s probably not a good direction to go.
I’m still so confused(through no fault of your own, I think you’re right, it just doesn’t fit in my head). Let me try to walk through my thought process.
I assume heritability of SAT score is probably different if you sample across USA, or just upper-mid class suburbs or just South Side Chicago, or just rural Eastern Europe, or just Malawi during a famine. Right? Given that environments are pretty radically different.
What heritability score are we using to determine if policy interventions matter or not? Is the first step to make sure that the region we want to improve has an environment that mimics ‘successful’ regions? Heritability would be very high in a homogenous environment(since that’s the only variation), but it goes down as more varied environments are added to the sample. Heritability is very high if we just look at rich area USA schools, lower if you sample all USA and even lower if we sample the whole world?
Also how is this linked to amplitude of effect? Super high heritability of SAT/IQ in say homogenous Denmark, but presumably the actual variation in scores is lower than in a global sample. Is there a way to say genetics account for +/- 5 points of IQ? So if you’re measuring IQs of 95-105 in your area that’s probably all genetic effects and policy interventions can’t do much?
Edit. I realize now that this is mostly Insub’s point below, but less coherent.
Pretty much. If an intervention is well outside of the set of experiences of your population, there’s probably a reason for that. Perhaps it’s just too new, but it’s likely that it’s inconsistent with the way the culture usually functions (its values as actually implemented) and/or has fairly obvious side effects.
The commenter you are replying to is right. Heritability shows how much of the current variation is genetic in origin, which shows whether the variability of nurture matters within that particular culture. If you want to successfully intervene, it needs to be either in something not very heritable, or with an intervention that is not a significant part of the current landscape of the society. (The fact that outside of context interventions may exist means heritability isn’t a measure of how genetic it is, but that wasn’t Sleeps Furiously’s point.)
Edit: Note, Sleeps Furiously had not replied to spkoc when I saw this and I wrote my response without refreshing.
But isn’t this exactly the mainstream intuition that the OP dissolves? My understanding:
a) Heritability measures don’t seem to make sense for really complex traits like intelligence.
b) Heritability measures are not stable outside the environmental conditions in which they were measured.
For instance, some people have sickle cell anemia, which helps them better survive malaria(but otherwise is slightly harmful). If you measure heritability of infant mortality in environment with malaria and then in environment without malaria you get opposite effects. You get a lighter case of malaria with it, so sickle cell probably positively correlates with intelligence if there’s malaria in the environment.
There’s also weird epigenetic multigenerational effects: https://www.nature.com/articles/s41467-018-07617-9 (quote is about a reference in this study)
I have this vague memory about reading an article claiming that grandparents’ access to food influenced their grandchildren’s height, moreso than their immediate childrens’, but I can’t seem to find it. Perhaps nonsense.
It is not that intuition. The mainstream intuition is that a high heritability means that variations in the thing that you’re measuring (height, SAT scores, infant mortality) is primarily affected by genetics and cannot be influenced by the environment. A better framing would say that high heritability means that variations in the thing that you’re measuring are not well explained by existing variation in the environment. To reframe, then, what I was going for above, a high heritibility is an upper bound on how much you can expect to improve a specific measure by playing around with existing policy levers, versus having to think outside the box and develop new policy levers.
So, again, pretend that SAT scores have a high measured variability in the US. (I think it’s actually closer to 50 than either extreme, but I don’t have off-hand an actual example of a measure that we might want to increase/reduce the variance of as a society that does have a high heritability.) We might look at nutrition, SES and education and ask whether we can manipulate these to significantly reduce the variance in height and/or SAT scores. Under the high heritability assumption, the answer is that this is very unlikely for both stats.
Again, this is without saying that high heritability means the existing policy levers are not having an effect right now. If we, as a country, stoppd feeding kids at age 5 and left them to fend for themselves, I would expect the survivors to be both shorter and have lower SAT scores than preceding generations. If we stopped sending kids to school, I would expect average SAT scores to drop and the variance to increase significantly. And nothing about heritability argues against any of that.
It also doesn’t mean that there are no policy levers that could have an effect. I am not biologist enough to know if the application of HGH to children on a large scale would increase average height, but what I can say is that heritability has nothing to say on the question, since it is currently an environmental variable with almost no variance itself.
Oops. Accidentally dropped a paragraph about whether you could increase height/SAT scores across the board with the existing policy levers. In that case, a high heritability doesn’t directly say that that’s unlikely, but you would at least have to expect to increase your policy setting to the point where most people are getting more of the nutrition or education or whatever than is currently a few standard deviations above average, since otherwise if less than that much of your policy was having an effect, you would expect to already see it in the heritability measurement. So heritability doesn’t say that feeding kids 10,000 calories a day or sending them to school for 12 hours a day won’t have effects on height/SAT scores, but as a general rule you’d be looking at such extreme interventions that it’s probably not a good direction to go.
I’m still so confused(through no fault of your own, I think you’re right, it just doesn’t fit in my head). Let me try to walk through my thought process.
I assume heritability of SAT score is probably different if you sample across USA, or just upper-mid class suburbs or just South Side Chicago, or just rural Eastern Europe, or just Malawi during a famine. Right? Given that environments are pretty radically different.
What heritability score are we using to determine if policy interventions matter or not? Is the first step to make sure that the region we want to improve has an environment that mimics ‘successful’ regions? Heritability would be very high in a homogenous environment(since that’s the only variation), but it goes down as more varied environments are added to the sample. Heritability is very high if we just look at rich area USA schools, lower if you sample all USA and even lower if we sample the whole world?
Also how is this linked to amplitude of effect? Super high heritability of SAT/IQ in say homogenous Denmark, but presumably the actual variation in scores is lower than in a global sample. Is there a way to say genetics account for +/- 5 points of IQ? So if you’re measuring IQs of 95-105 in your area that’s probably all genetic effects and policy interventions can’t do much?
Edit. I realize now that this is mostly Insub’s point below, but less coherent.
Pretty much. If an intervention is well outside of the set of experiences of your population, there’s probably a reason for that. Perhaps it’s just too new, but it’s likely that it’s inconsistent with the way the culture usually functions (its values as actually implemented) and/or has fairly obvious side effects.
The commenter you are replying to is right. Heritability shows how much of the current variation is genetic in origin, which shows whether the variability of nurture matters within that particular culture. If you want to successfully intervene, it needs to be either in something not very heritable, or with an intervention that is not a significant part of the current landscape of the society. (The fact that outside of context interventions may exist means heritability isn’t a measure of how genetic it is, but that wasn’t Sleeps Furiously’s point.)
Edit: Note, Sleeps Furiously had not replied to spkoc when I saw this and I wrote my response without refreshing.